Download brain and cranial nerves

BRAIN AND CRANIAL NERVES
1. Introduction:
a. Brain is the center of;
Registering sensation.
Store information.
Making decision.
Taking action.
Center for intellect and emotion.
Center for behavior and memory.
Directs our behavior towards others
b. How principal parts of the brain relate to the spinal
cord & to 12 pairs of cranial nerves.
2. Overview of brain organization:
Principal parts of the brain are: Brain stem
Diencephalon
Cerebrum &
Cerebellum
a. Blood flow and Blood-brain barrier:
i. --Brain comprises only about 2% of the body
weight.
--Amount of oxygen brain uses varies with the degree
of mental activity.
 Blood supply of the brain is from cerebral arterial
circle( circle of Willis) at the base of the brain.
ii. Interruption of oxygen supply to the brain can result
in weakening, permanent damage or death of brain
cells.
iii. The supply of glucose to the brain must be
adequate as glucose deficiency may produce mental
confusion, dizziness, convulsion and unconsciousness.
iv. A blood-brain barrier (BBB) protects brain cells
from harmful substances and pathogens by serving as
a selective barrier to prevent passage of many
substances from the blood to the brain.
 Any injury, inflammation or toxins can cause
breakdown of the BBB—permitting the passage of
normally restricted substances into the brain tissue.
3. Cerebrospinal fluid: production and circulation:
a. Ventricles: CSF is a clear & colorless fluid that
protects the brain & spinal cord. It also carries
oxygen, glucose & other needed chemical from the
blood to neurons & neuroglia.
b. Ventricles are CSF filled cavities within the brain
that contributes to homeostasis. CSF is formed by
filtration from network capillaries called Choroid
plexus & circulates through the subarachnoid space,
ventricles & central canal.
c. Most of the fluid is absorbed by the arachnoid villi
of the superior sagittal sinus. Rate of formation &
absorption is same and so maintain a relatively
constant CSF volume & pressure.
d. Hydrocephalus: If CSF cannot circulate & drain
properly due to some obstruction in the ventricle or
in subarachnoid space, it leads to raised intracranial
pressure.
4. The brain stem:
a. Medulla oblongata:
--Contain both motor and sensory tracts.
--Also contain the nuclei of origin for cranial nerves
viii through xii
--Structurally it contains pyramids & olivary
nucleus. Pyramid is formed by decussation of
pyramidal fibers, which supply the skeletal muscles
of the opposite side.
Medulla oblongata (cont.)
 Functionally medulla is responsible for regulation
of heart rate, regulation of respiratory rate,
vasoconstriction, swallowing, coughing, vomiting
sneezing & hiccup.
 Injury to medulla can lead to serious consequences.
b. Pons:
--Located superior to medulla.
--it relays nerve impulses related to voluntary skeletal
movements from the cerebral cortex to the cerebellum.
--it also contains pneumotaxic & apneustic center
which help control respiration.
--it contains nuclei of cranial nerves v through vii &
the vestibular branch of viii nerve.
c. Midbrain:
--it connects the pons and diencephalon.
--it conveys motor impulses from cerebral cortex to
cerebellum.
--it sends sensory impulses from the spinal cord to the
thalamus and regulate auditory and visual reflexes.
--it contains nuclei of origin for cranial nerves iii & iv.
--it helps regulate muscle tone, alert the cortex to
incoming sensory signals(reticular activating
system,RAS)—is also responsible for maintaining
consciousness and awakening from sleep.
5. The cerebellum:
--Occupies the inferior and posterior aspect of the
cranial cavity and consists of two hemispheres and a
central vermis.
--it is attached to the brain stem by three pairs of
cerebellar peduncles.
--it functions in the coordination of skeletal muscle
contraction and in the maintenance of muscle tone,
posture & balance.
6. Diencephalon:
a. Thalamus: situated superior to the mid-brain and
contains nuclei that serves as relay stations for all
sensory impulses (except smell) to the cerebral
cortex.
--it also registers conscious recognition of pain and
temperature and some awareness of light touch &
pressure—it plays an essential role in awareness &
acquisition of knowledge which is termed Cognition.
7. The cerebrum:
--it is the largest part of the brain.
--the surface layer is composed of gray matter, which
contains billions of neurons.
--cortex contains gyri (convolutions) deep grooves—
called fissures & shallow grooves—sulcus.
--beneath the cortex lies the cerebral white matter,
tracts that connect part of the brain with itself and
other parts of the NS..
A. Lobes:
--each cerebral hemisphere has four lobes.
Frontal
Parietal
Temporal
Occipital.
B. White matter:
--white matter is under the cortex & consists
of myelinated axons running in three principal
directions---association fiber
Commissural fiber
Projection fiber.
C. Basal ganglia:
--they are paired masses of gray matter in each
cerebral hemisphere.
--they are responsible for planning and control of
muscular movements.
D. Limbic System:
--Limbic system is found in the cerebral hemisphere &
in diencephalon.
--it functions in emotional aspect of behavior, memory
& is associated with pleasure and pain.
8. Functional aspect of cerebral cortex:
A. Specific types of sensory, motor & integrative
signals are processed in certain cerebral regions.
i. Sensory areas:
--they are concerned with the reception and
interpretation of sensory impulses.
--Sensory areas are:
Primary somatosensory area.
Primary visual area.
Primary auditory area.
Primary gustatory area.
ii. Motor areas:
--control and govern muscular movements
--areas are:
primary motor area.
Broca’s speech area
iii. Association areas:
--they are concerned with complex integrative
functions, such as memory, emotions,
reasoning, will, judgement, personality, traits
& intelligence.
--Association areas are:
Somatosensory association area.
Language area.
Visceral association area.
Auditory association area.
Wernicke’s area.
9. Hemisphere lateralization:
--two hemispheres of the cerebrum are not
bilaterally symmetrical.(either anatomically or
functionally) and have functional asymmetry.
--the left hemisphere is more important for righthanded person—for spoken or written language,
numerical & scientific skills.
--the right hemisphere is more important for lefthanded person, musical & artistic awareness, apace
& pattern perception, imagination, generating
mental images of sight, sound & touch, taste &
smell.
10. Brain waves:
- --Electrical potential generated by brain cells—
called brain waves.
--Brain waves generated by the cerebral cortex called
Electroencephalogram (EEG)
--EEG is used to diagnose:
Tumors.
Trauma, hematoma
Epilepsy. & other seizure disorders.
Degenerative diseases
Period of unconsciousness.& confusion.
Sleep & wakefulness.
Confirming brain death.(complete absence of
brain waves)
--There are four kinds of brain waves can be
recorded in normal individual.
Alpha-Normal,wake, resting(eye closed)
Beta- when NS active, high mental activity
Theta- emotional stress, in adult, child
Delta- occurs only in deep sleep (Normal)
In wake adult, it shows brain damage
11. Cranial nerves:
--12 pairs of cranial nerves originate from the CNS
--they are named on the basis of distribution &
numbered by order of attachment to the brain.
--Some cranial nerves are only sensory(i, ii, viii)
and the rest are mixed nerves as they contain both
motor and sensory fibers.
12. Aging and the nervous system:
--Age related effects are:
--Loss of neurons
--Decreased capacity for sending impulse to
& from brain
--Diminished processing of information.
Decreased conduction velocity.
--Slowing of voluntary motor movements &
reflex time.
Degenerating changes involving sense
organs—vision, hearing, taste, smell &
touch.
13. Disorders:
A. Most common: Cerebrovascular accidents
,CVA(stroke).
--it is of two principal types:
i. Ischemic(common)
ii. Haemorrhagic.
--Common causes of CVA are:
Intracranial hemorrhage
Emboli & aetherosclerosis.
B. Transient Ischemic attack (TIA)
--Temporary cerebral dysfunction due to impaired
flow of blood, due to blood clot & aetherosclerosis.
C. Alzheimer’s disease:
--Cause not known
--Involves widespread intellectual impairment,
personality disorder.
--Has no cure at present
Brain and Cranial Nerves
Topics:
1. Introduction.
2. Overview of brain organization.
3. Cerebrospinal fluid—production & circulation.
4. The brain stem.
a. Medulla Oblongata.
b. Midbrain.
c. Pons
5. The cerebellum.
6. Diencephalon.
Thalamus
7. The cerebrum
a. Lobes.
b. White matter.
c. Basal ganglia.
d. Limbic system.
8. Functional aspect of cerebral cortex.
9. Hemisphere localization.
10. Brain waves.
11. Cranial nerves.
12. Aging and nervous system.
13. Disorders.